In recent years, the demand for an increase in capacity and an increase in speed of a radio communication shows a great rise, and researches on the method of improving further an effective utilization efficiency of finite frequency resources are done eagerly. As one method of them, the approach for utilizing a spatial domain commands public attention. One of the technologies to utilize a spatial domain is the adaptive array antenna (adaptive antenna). This adaptive antenna can receive strongly a desired signal arriving from the desired direction by adjusting an amplitude and a phase by means of a weighting factor (this weighting factor is referred to as a “weight” hereinafter) by which the received signal is multiplied, and can suppress an interference component signal such as a multipath interference, a co-channel interference, or the like. A channel capacity of the communication system can be improved by such interference suppressing effect.
Also, as another technology utilizing a spatial domain, there is the space division multiplexing (abbreviated as “SDM” hereinafter) technology to transmit different data sequences to the same terminal through the physical channel with the same symbol at the same time and the same frequency by utilizing a spatial orthogonality on the channel. The SDM technology is given as an information disclosure in Non-Patent Literature 1, for example. The SDM transmission can be implemented in a propagation environment in which a correlation of the received signal between the antennas is low, by providing a plurality of antenna elements to both a transmitter and a receiver. In this case, the transmitter transmits different data sequences through the physical channel with the same symbol at the same time and the same frequency from plural antennas every antenna element, while the receiver separates signals received through plural antennas provided to the receiver based on the estimate value of the channel characteristic and receives the signals. As a result, an increase in speed of the transmission can be attained by using a plurality of SDM channels without a multilevel modulation. In the case where the SDM transmission is carried out, when the transmitter and the receiver are equipped with antennas in the same number, an increase of channel capacity that is proportional to the number of antennas can be achieved in an environment in which a large number of diffusion bodies exist between the transmitter and the receiver in sufficient S/N (signal to noise ratio) condition.    Non-Patent Literature 1: G. J. Forschini, “Layered space-time architecture for wireless communication in a fading environment when using multi-element antennas”, Bell Labs Tech. J., pp. 41-59, autumn 1996